This study combined demographic and institutional explanations of women's employment, describing and explaining the degree to which mothers in industrialized societies are less likely to be employed than women without children. A large number of cross-sectional surveys were pooled, covering 18 Organisation for Economic Co-Operation and Development countries, 192,484 observations, and 305 country-years between 1975 and 1999. These data were merged with measures of institutional context and analyzed with multilevel logistic regression. The results indicate that, over time, women were increasingly likely to combine motherhood and employment in many, but not all, countries. Both mothers and women without children were more likely to be employed in societies with a large service sector and low unemployment. The employment of women without children was generally unaffected by family policies. Mothers were more likely to be employed in societies with extensive reconciliation policies and limited family allowances.